Thermionic device and circuit therefor



'1991111101119 nEvIcE AND CIRCUIT 911111199011Y 1i1doot.9. 1931 N kl e ATTORNEY Patented Nov. 13, 1934 UNITED STATES PAT ENT OFFICE THERMIONIC DEVICE ANI) CIRCUIT THEREFOR York Application October 9,

15 Claims.

This invention relates to a thermionic device and circuit therefor, which =may be used to produce sustained oscillations as employed' in connection with radio, telegraphy and telephony,

and for other purposes Where such devices and circuits are or may be employed.

An object of the invention is to provide means for generating continuous high frequency oscillations having a frequency stability equal or superior to the best crystal controlled oscillators without employing crystals.

Another object is to provide means for generating continuous high frequency oscillations that does not require temperature control and the l5 numerous other precautions necessary inthe case of otherforms of oscillators.

Another object is to provide means for generating continuous .high frequency oscillations without employing a thermionic tube'operating as the result of secondary electron emission, such as the well-known Dynatron.

' Another object is to provide means for generating continuous high frequency oscillations that does not operate by reason of feed-back or regen- 5 eration.

y A further object is to provide a tube and circuit therefor that is simple and cheap to manufacture.

Other objects will be apparent from the following specification, in which by way of illustration, one'embodiment of the invention is de-l scribed.

All self-excited oscillators, particularly those of the thermionic or vacuum tube type depend upon the presence of a negative resistance characteristic for operation.

In the case of the well-known Dynatron type this characteristic is obtained as the result of secondary emission. At certain critical energy values of the impacting electrons, reflection, reemission and inverse.photo.electric effects combine with the changev in the potential gradient between the grid and the plate of the tube and the sum of these effects gradually reduces the electron stream flowing from grid to plate and throughthe external circuit connected to the lat ter. This inversion of current continues until the negative current predominates and approaches its maximum saturation value at a point below the applied grid potential. One of the reasons why this principle has not come into extended use is because of manufacturing difficulties in connection with controlling the re-emission properties of the metal surfaces within the'tubes;

1931, Serial No. 567,805

which diiliculties are not present in the construction embodied inthe present invention.

In the case of tubes employing feed-back or regeneration, the diillculties of securing continuous and accurate regulation are well known and are not herein referred to in detail as it will be obvious from the following specification how the present invention eliminates these diiiculties.

While arc oscillators have al negative voltage characteristic they are not referred to herein'as they are practically obsolete commercially and have no bearing on the instant invention.

In the accompanying drawing:

Figure 1 is a diagrammaticcross-sectional view `of a negative resistance tube, together with the vattendant circuit necessary for the production of sustained oscillations, illustrating this invention;

Figure 2 is'a cross-sectional view of thetube 0n the line 2-2, Figure 1; andv Figure 3 is a cross-sectional view of the tube on the line 3 3, Figure 1.

The numeral 10 denotes a fllamentary type of cathode element in the form of a double helix but this may be of any suitable shape and may be any form of electron emitter. This is surrounded by a cylindrical metal shield element 11 having a closed outer end opposite the outer end of the cathode, said end having an aperture 11a therein (which may be a relatively long and narrow slot) in the center thereof for the purpose of substantially confining the electron emission from the cathode to a relatively small area. This shield forms a chamber surrounding the cathode and is electrically connected as shown at 12 to the cathode circuit, the terminals of which are indicated at 13, 14.

The cylindrical metallic accelerating element 15 (hereinafter termed the accelerator) is supported in any suitablemanner, such as by the metal supports 16, 17 which extend along the sides of the cathode and are secured to a metallic band 18 supported in the neck of the glass tube or bulb 19. This band forms the circuit terminal for the accelerator. This accelerator has a tubular neck 15b extending outwardly intov the element 22 as shown andhas a clod end toward the cathode, which end has an opening or slot 15a therein as shown and'correspondingto the opening or aperture 11a in the shield element 11.

A target element or anode 20 is supported in the tube by means of a terminal 21 and is positioned' at one end of the tubular negative resistance elementl 22, as shown in Figure 1.` A

'Ihe element 22 is supported upon the terminal 23 imbeddedin the Wall of the tube.

'Ihe construction and arrangement of the elements just described can be varied within wide limits and it will beunderstood that all of these elements are enclosed in the usual glass envelope or bulb 19, which is evacuated in the usual manner, the various terminals of the tube being of any suitable type and extending therefrom sufficiently to enable the necessary circuit connections to be made thereto.

The tube is vconnected up in circuit with sources of energy and the other instrumentalities as shown in Figure 1, wherein the numeral 24 designates the cathode current supply (which may be the usual type of batry) the positive pole of which is connected to terminal 14 via Wire 25. The remaining filament terminal 13 (which also connects to the shield element 11) is connected via wire 26 with the negative pole of battery 24 and the ground 27, or is otherwise maintained at ground potential.

A tank circuit comprising the inductance L1 and capacity C1 is connected to the negative resistance element 22 via terminal 23. A conductor 28 connects the tank circuit to a current supply such as the usual battery 29, and may be tapped therein to secure any desired voltage thereof. The negative side of this battery is connected to the negative side of battery 24 and to ground 27. This tank circuit determines the period of oscillation.

'I'he accelerating element 17, the terminal of which is the band 18, connects via wire 31 with the battery 29, and may be tapped therein at any point to secure any desired voltage thereof.

A bypass condenser C2 is connected to the tank circuit and ground, as shown.

The anode target element 20 is connected va its terminal 21 with the inductance L2 which is connected via conductor 32 with the positive side of the battery 29. L2 is inductively coupled to L3 in the output circuit 36 of the oscillator.

In operation, the tube being connected as just described and as shown in Figure 1, L1-C1, C2 and .L2- L3 may be disconnected and a static characteristic curve taken by inserting a milliammeter in place of L1-C1, the negative voltagecurrent eiect being obtained through the circuit including terminal 23 and conductor 28. It will be assumed that the voltages of the batteries 24 and 29 remain relatively xed and that the voltage of the circuit (via the variable tap on the battery end of conductor 28) is capable of being varied over the entire range of the voltage of the battery 29 from zero to maximum.

With a small value of voltage .from battery 29 applied to the element 22 it will be found that the stream of electrons leaving the cathode 10 are substantially conned as to cross-sectional area to the openings 11a and 15a, and are pulled through these openings by reason of the comparatively high positive potential existing on the acoelerator 15 which is connected via conductor 31 to a point in the battery 29 of greater positive potential than that existing on element 22. The accelerator also serves to focus the stream f electrons accurately through the center of the negative resistance element 22. i,

The electrons passing into element 22 will assume therein somewhat the path indicated by the curved dotted lines 33, 34, which indicate that the initial velocity imparted to the electrons by the accelerator 15 is soon lost and as a result the electrons disperse and are attracted to the element 22, causing appreciable current to flow through the circuit 28-23 and the meter connected therein.

If now the voltage on element 22 is increased, the electron path becomes less like 33, 34 and more nearly straight as` shown by the dotted line 35. That is to say, instead of the electrons diverging, due to a loss of velocity as they pass through the cylindrical negative resistance element 22, they are, due to the presence of the higher voltage on 22, caused to continue more nearly in a straight line to the target or anode 20. Thus an electron stream is established from the cath- 0de 10 to the anode 20 which is accelerated by the accelerating means 15, and attracted by the means 22.

As the voltage on the element 22 is further increased fewer electrons collect on 22 but continue on to the anode 20, from which it is apparent that the circuit from the terminal 23 through the meter and conductor 28 will have a negative voltage-current characteristic, for, as the voltage through this circuit increases, the current actually decreases due to the phenomena just described.

The foregoing tests having been made to determine the' negative current characteristic of the oscillator, it only remains to disconnect the meter and introduce into the circuit 28-23 the inductance L1 and the capacity C1 in order to generate sustained oscillations. As the action of Ll-Cl on the circuit is Well understood it will not be described in detail. The negative resistance value of the tube should be equal or less than-the resistance of the tank circuit Ll-Cl, and the vfrequency of the generated oscillations can be varied at will by varying the capacity C1 which may be a Variable condenser of any suitable construction.

In use, the output circuit 36 could be connected to 23 and 28 and the anode 20 connected directly to the positive pole of battery 29, but in practice it has been found that by coupling the output by means of the inductance L2--L3 in the anode circuit that variations in load in the output circuit 36 have a negligible reaction on the tank circuit L1, C1 and for this reason, have a negligible inuence on the frequency of the generated oscillations.

The frequency of the generated oscillations us- Q .tal and temperature controls unnecessary.

It will also be observed that this invention obtains high frequency oscillations which are not the result of secondary emission in the tube, feed-back or regeneration and that the tube is relatively simple and easy to manufacture. Thus the objects heretofore mentioned are attained as herein disclosed.

Although the invention has been disclosed in connection with the specific details of preferred embodiments thereof, it must be understood that such details are not intended to be limitative of the invention except in so far as set accompanying claims.

What is claimed is:

1. In a device of the character described, a cathode, an anode, a member adapted to shield said cathode and direct an electron stream therefrom ina predetermined path, means surroundforth in the ing a portion of said path and connected to a source of current whereby the movement of electrons therein toward said anode is accelerated, and control means adjacent said path adapted to attract or repel electrons therefrom, said control means connected to a steady source of positive potential with respect to said cathode, the magnitude of said positive potential being adjusted to a Value from which positive increments of said potential cause said electron stream to be repelled from .said control element and negative increments cause said electron stream to be attracted to said controlelement.

2. In a device of the character described, a cathode, a shield surrounding said cathode and adapted to define the electron stream emitted therefrom, an anode, a source of voltage connected between saidA cathode and anode, positive to anode, for establishingv an electron stream between said anode and cathode, an element for accelerating the ow of said stream, and a control element disposed along and surrounding the path of said electron stream between said accelerating element and said anode, said control element also being connected to a source of positive voltage with return to said cathode, the voltage to said control element being so adjusted with respect to said anode voltage and the relationship of said control element to said electron stream that a positive increase in said control element voltage causes a decrease in electron current through the circuit attached to said control element.

3. In a device of the character described, anode and cathode elements, a shield about one of said elements connected thereto and adapted to define the electron ow therefrom to a substantially long and narrow path, means adjacent said path for accelerating the flow of electrons therealong from one of said elements to the other, a control member surrounding a portion of said path between said accelerating means and said anode, said anode and control element having positive voltages applied thereto of such proportions to vone another that the current through the circuit attached to said control element will exhibit a negative characteristic with respect to the applied voltage, and an electrical resonant circuit consisting of inductance and capacity being connected in series with said control element circuit and adapted to provide for the generation of sustained oscillations of a period substantially equal to the natural resonant period of said tuned circuit.

' 4. In a device of the character described, anode and cathode elements, a shield about one of said elements connected thereto and adapted to define the electron ilow therefrom to a substantially longand narrow path, means adjacent said path for accelerating the flow of electrons therealong from one of said elements to the other. and a control element surrounding a portion of said path between said accelerating means and said anode, said accelerating means, control element and anode being connected to positive sources of potential with common, returns to said cathode, the magnitude of said potentials being adjusted with respect to one another so that a negative voltage-current characteristic will be obtained through the circuit attached to said control element for relatively small changes of potential applied thereto.

5. In a device of the character described, a cathode, an anodeLmeans for establishing an electron stream therebetween, means between said anode and cathode for defining the crosssectional area of said stream, an electron a'c-- celerating element disposed beyond said electron stream deiining means, and a control element disposed between said accelerating element and said anode having substantially -the same cross sectional shape as said electron stream and spaced closely thereto, said accelerating element, control element and anode being connected to sources of positive potential with returns to cathode, said potentials adjusted to project said electron stream between said cathode and anode concentrically through `said control element such that when the potential applied thereto is decreased a greater number of electrons from said stream will be attracted to said control element and less will reach said anode by reason of lessened accelerating eiect of said control element, thereby obtaining a negative voltage-current relationship for changes in potential applied to said control element.

6. In a device of the character described, a cathode, an anode, a source of potential connected therebetween, positiveA to anode, for establishing an electron stream therebetween, means between said anode and cathode for dening the cross-sectional area of said stream, means adapted to act on the defined stream yto accelerate said electron stream between said cathode and said anode, and a control element of substantially the same cross sectional shape as said defined electron stream and arranged concentrically about said stream between said accelerating means and said anode and having a source of positive potential with respect to cathode connected thereto to further accelerate said electron stream,.the magnitude of said potential being adjusted to a value such that a further increase in said potentialwill cause a decrease in current through said control element and a decrease in potential will cause an increase in current, the current through said anode varying in an inverse relation to the current through said control element.

7. In a device of the character described, a cathode, an anode, an electron stream therebetween, a shield about said cathode adapted to define the cross-sectional area of said stream, means adjacent said shield to accelerate the speed of said electrons, and a control element adjacent said anode adapted to attract said electrons, said control element being of substantially the same cross sectional shape as said dened electron stream and disposed in longitudinal close relationship to said electron stream, said control element and said anode being connected to/positive sources of potential said circuits returning to said cathode, said potentials being adjusted so that said control element normally acts to further accelerate said electron stream therethrough normal adjusted value, causing a greater num- 'f ber of the total available electrons to be attracted to said anode and less to said control element, conversely, decreases in potential from the normal adjusted value, causing a greater portion of said electrons to be attracted to said control elef ment by reason of Iessenedacceleration, and few-`r er to reach said anode, the sum of said control element currentand said anode current being a constant overy the operable rangeof control'ele-r mentvoltage, the operable rrange being definedr yas that rrange of applied control element voltages over whichy a negativey voltage-current relationship is obtained.

f f i8; `In a `device ofk the` character described, a

cathode, an anode, a, shield about said cathoder adapted to denefa cross-sectional area ofy the electron stream emitted therefrom, an accelerator element positioned adjacentr said shield, said element having an aperture adapted yto ypermit continuous manner at a period determined sub--y stantiallyiby the rnatural electrical period of said an yaccelerating relerner1tanegative resistance- 1 tunedcircuitby reason ofthe negative 'voltage--r current characteristic` exhibited by said second element, said tuned electrical circuit possessing an eiective parallel resistance equal toor greater than the value of negative'resistance obtained through said second element c c c 9,. In combination, ra thermionic device having an anode, a cathode, a shieldraboutthe cathode,

element, a sourcefof yenergyy connected tosaid cathode andshielda source :of energy connected rto f said accelerator, negative resistance element and anode, and a tank circuit consisting of inductance and capacity in parallel in the connection between said negative resistance element and said last source of energy, said cathode being heated to provide a source of electrons and thereby establishing a stream of electrons between said cathode and said anode, said anode being made positive with respect to said cathode, said electron stream passing consecutively from cathode through said cathode shield, accelerating element, negative resistance element to said anode, said cathode shield having an orifice to permit the passage of electrons only in the form of a stream of predetermined cross section, said accelerating element and negative resistance element being in the form of hollow tubes having a( cross section of substantially the same form as said cathode shield orifice but of slightly larger dimensions to enable the passage of said electron stream therethrough without appreciable collision of said electron stream with said accelerating element and said negative resistance element, the potential applied'to said negative resistance element Ibeing normally adjusted with respect to the potentials applied to said accelerating element and said anode so that a negative voltage-cur-v rent characteristic will'be exhibited through said tank circuit connected to said negative resistance.

element and by reason of which a condition of sustained -oscillation is obtained in said tank circuit, the period of said oscillation being determined substantially by the electrical constants of said tank circuit.

10. In combination, a thermionic device having an anode, a cathode, a shield about said cathode,

rsaid shieldihaving an oriiceto permit the passage of electrons from said cathode to' said anode f f i f in the formof a stream of a cross section determined rbythe shape and size of said orifice in said shield, a source ofy yenergy yconnected vto said f,

cathode and shield, a control element positioned rbietweenfsaid shield and anode, a tank circuit containing an inductance and capacityconnected f l torssaid control element, a source of energy conrnected to said tank circuit, and a connection betweeny said cathode and'said last source of energy,

said anode and rcontrol element being positive with respect to said cathode, said control element being in the rform of a hollow tube of substantially the same cross sectional shape as the orifice in said shield but of slightly largerdimensions to c permit the passage ofy said electron stream theret relation to the applied voltage said negative voltey age-current characteristicibeing obtained because an increase in said control elementipotential fromy said coadjusted value causes greater acceleration of said electron streamthrough said control ele ment thereby causing'fewery electronstor collide n with said control element, said increase in potenitial acting'to converge said electron stream conversely, a decrease in saidcontrol element ypo-r tential from said coadjusted kvalue will cause a deceleration of said electron stream thereby causing divergence of saidfelectronfstream andr consequently greater collision of-said electron stream ywith said controlelement, the numerical value of negative resistance obtainedthrough said control f element being equal to or less than the effective f parallel yresistance of said tank circuit connected thereto, the current through said tank circuit andy said control element thereby 4,being caused yto oscillate in a sustained manner, the period of said oscillations being determined substantially by the electrical constant of said tank circuit.

l1. In combination, a thermionic device having an anode, a cathode,.a shield about the cathode, a source of energy connected to said cathode and anode, positive to said anode, an accelerating element, a source of energy having its positive pole connected to said element and its negative pole connected to said cathode, a negative resistance element connected to said last source of energy but of lesser positive potential than said accelerating element, and a connection from the positive pole of said last source of energy to said anode, said connection having an inductance connected serially therein, said shield having an aperture of predetermined shape and size to allow the passage of electrons from said cathode to saidanode in the form of a stream of substantially the same shape and size as the aperture in said shield, said cathode being heated to supply free electrons, said accelerating element being in the form of a hollow tube of the same cross sectional shape as said shield aperture but of slightly'larger dimensions and disposed next to said shield aperture, said negative resistance element also being in the form of a hollow tube of the same cross sectional shape as said shield aperture but of slightly larger cross sectional dimensions than said accelerating element, said negative resistance element disposed between said accelerating element and said anode, said electron stream being caused to traverse concentrically through the center of said accelerating element and said negative resistance element, the magnitude of potentials applied to said accelerating element, negative resistance element and anode being coadjusted to produce a negative voltage-current characteristic through said negative resistance element for small variations of said negative resistance element potential from said coadjusted value the current through said negative resistance element thereby also varying inversely with the current through said anode, said negative resistance element having connected -in series therewith an electrically resonant circuit consisting of inductance and capacity in parallel, the current through said negative resistance' element and resonant circuit being caused to oscillate in a sustained manner, the period of such oscillations being determined substantially by the constants of said resonant circuit, the current through said anode also being caused to vary at a like period but 180 out of phase with the current through said negative resistance element, said inductance in series with said anode providing a means for coupling a y work circuit to said ysource of oscillations in said anode circuit.

12. In combination, a thermionic device having an anode, a cathode, a shield about the cathode,

, an accelerating element, a negative resistance element, a source of energy connected to said cathode and negative resistance element, the positive pole to said negative resistance element and having its negative pole grounded, a source ofenergy connected to said accelerator and having its negative pole grounded, said cathode also being grounded, a tank circuit comprising inductance and capacity in the connection between said negative resistance element and said first source of energy, and a bypass condenser connected between the low potential side of said tank circuit and ground, said anode made positive with respect to said cathode, said cathode being heated to provide for the emission of free electrons therefrom, said shield having an aperture therein to allow the establishment of an electron stream of predetermined cross sectional area, between said ,crease with further increase in said potential from aforementioned value of normal adjustment, increases from said normal potential value causing greater acceleration of said electron stream through vsaid negative resistance element and consequently less collision of said streaml therewith, decreases from said normal potential value causing deceleration of said electronstream and consequently greater collision of said electron stream with said negative resistance element in its passage therethrough due to lowered velocity of said electrons of said stream, said tank circuit connected to said negative resistance element thereby causing the generation of continuous oscillationsby reason of said negative voltagecurrent eiect through said attached negative resistance element, said period of oscillation being determined by the natural electrical period of said tank circuit. v

13. In combination, thermionic device having an anode, a cathode, a shield, a nega-tive resistance element, an accelerating element, sources of energy connected to said elements in order to produce astream of electrons and cause the same to flow in a controlled manner from the cathode to the anode, a tank circuit connected to said negative resistance element, and an output circuit inductively coupled in the anode circuit, said shield substantially surrounding said cathode and having an aperture therein to direct said electron stream toward said anode and conning said stream to denite cross sectional shape and area,

said accelerating element being in the form of a hollow tube and disposed 'adjacent said aperture in said shield, said negative resistance element also being in the form of a hollow tube and disposed between said accelerating element and said anode, the inside openings of said accelerating element and said negative resistance element being substantially of the same shape as the aperture in said shield but yof larger dimensions to allow the passage of said electron stream normally therethrough in an unobstructed manner, said accelerating element, negative resistance element and `anode being all made positive with respect to said cathode and the magnitude of applied potentials being coadjusted to such values that for relatively small changes of potential from said coadjusted value of said negative resistance element, a negative voltage-current relationship will be obtained, increases in said potential causing greater velocity to be imparted to said electrons passing through said negative resistance element and resulting in less attraction ,of said electrons to said element, and conversely decreases in said potential lowering the velocity ofsaid electrons and resulting in greater attraction between said electrons and said negative resistance element, said phenomena resulting in a negative voltage-current characteristic through said negative resistance element thus allowing said-tank circuit, connected thereto, to operate in a state of sustained oscillation, the negative resistance value of said negative resistance element being equal to or less than the effective resistanceof said tank circuit.

14. In combination, a thermionic device comprising a vacuum tube having therein a plurality of elements, two of which constitute cathode and anode, said cathode being caused to emit free electrons, a, suitable source of potential between cathode and anode to establish an electron stream therebetween, two other elements forming chambers to entirely surround and enclose the electron stream owing from the anode to the cathode of the tube, means including a tank circuit connected to one of said elements causing the tube to oscillate, and an output circuit inductively coupled to the anode of the tube, said last two elements being connected to positive sources of potential with respect to said cathode, thev element to which said tank circuit is connected having a negative voltage-current relationship therethrough by which means the current through said tank circuit is enabled to oscillate at a period determined by the electrical constantsof said tank circuit, said negative voltage-current relation being caused by the control of said tank circuit element potential on the velocity of said electron stream therethrough,greater potential increasing said velocity and lessening attraction of said element on said electron stream, lesser potentials causing lowered velocity and greater attraction of said electron stream to said element, said attraction of said electron stream to said tank circuit element being inversely proportional to the square of the velocity of the electrons in said stream.,

15. A thermionic device comprising a vacuum -tube having a cathode therein, an apertured shield about the cathode, an accelerating element having an aperture therein registering with the aperture in said shield, means for causing the cathode to emit electrons, means for attracting said electrons through said apertures and into the interior of said accelerating element, a negative resistance element adjacent the outlet from said accelerating element and surrounding a portion thereof, and an anode adjacent said negative resistance element, said accelerating element, negative resistance element and anode being connected to a positive source of potential with relnegative resistance element connected thereto,

said resonant circuit thereby being caused to oscillate in a sustained manner.

EARL L. KOCH. 

